Dear ihar,
the Japanease version of the PRS-650 is delivered with firmware version 1.0.00.12200. On the japanease SONY homepage is an update to a newer version available. I installed this update on my device. But I think for the later conversion this was not important.
My main problem until now is that the problem with the device IDs (e.g DRM) is not solved. I am working on a solution.
So from my side I can not provide at this time the software/firmware I installed on my device, because this contains secret information from a third person.

My PRS650 has now the firmware version 1.0.00.14080. As far as I know this is the latest international version.
To convert my device I used a complete dump of a international device. The problem is that the device ID is coded somewhere in the flash and I don't know where. The result is now that 2 devices exits with the same ID.
To try to find out the block with device ID by changing one after each other back can result very fast in a bricked device. So this is also no solution. That is my problem.

I am in the exact same situation, I own a J-PRS-650 and would like to switch to a custom firmware supporting dictionaries.
The lack of "while reading" dictionary access is very frustrating in the original firmware when english is not your mother tongue ...
Is there anyone willing to share a/his international prs 650 firmware ? So I can go through the same process and finally update to a dictionary friendly prs ?